Challenges from Soil Variability, Johan Castberg Field, Barents Sea

Abstract

As development concepts for the Johan Castberg Field matured, new locations required soil data. A harder layer has been identified from previous soil data and mapped on seismic profiles as Seismic Unit II. This layer may cause refusal of suction anchor penetration and should ideally be avoided. Predictions of the depth to this layer both along and between seismic profiles were used to optimize suction anchor locations to be investigated during the 2018 soil investigation. This campaign was furthermore optimized by taking earlier laboratory testing into consideration. The Nkt factors were given special attention and found not to vary much in the topmost soil layers. Greater emphasis could therefore be put on acquiring CPTU data, and to use these previously determined Nkt factors to find the soil strength. The predictions of the depths to the top of Seismic Unit II were in general agreement with the data acquired during the 2018 investigation. The emphasis on collecting CPTU data and combining these with experience from the previous soil testing results saved both ship time and laboratory costs.